1. Filed of the Invention
This invention relates to a device for detecting states of cutting of a metal sheet by laser beam machinery, in particular to a device for detecting finish of piercing, a device for detecting improper cutting, and a device for detecting finish of piercing and improper cutting.
2. Description of the Prior Art
It is desirable to detect the cutting state in cutting a metal sheet by laser beam machinery. Such cutting is carried out quickly, easily, and safely by detecting finish of piercing and improper cutting states such as grousing and burning.
Piercing must be done before starting cutting of a metal sheet by laser beam machinery. The finishing time of piercing is a period form opening of a shutter of the laser beam machinery for applying laser beam onto a metal sheet to penetrating of the metal sheet by the laser beam. The finishing time depends on states of a generator such as the power and mode, of a work such as thickness, composition, and surface condition, and of the machinery such as a mirror and a cutting lens. For example, in the case of a standard steel plate, the finishing time is 5 seconds when such elements are in the best condition and 12.5 seconds when worst, resulting in the difference of 7.5 seconds.
In the conventional laser beam machining, a sufficient time is given for the laser beam machinery to afford the finish of piercing because piercing may carried out under the worst condition. Therefore, the machinery is usually waiting until the given time is over after piercing has already completed. Furthermore, there is no device to detect the finish of piercing. Hence, the machinery must wait for a certain time causing a lot of time loss.
In addition, an automatic programming device or operator must know the information about the finishing time of piercing for every workpiece since the finishing time is different depending on material and thickness of the workpiece. Furthermore, the information about the finishing time is necessary for NC library or statement. Therefore, memory is used, and machining speed is delayed.
In cutting of a metal sheet by laser beam machinery, the metal sheet is cut properly when laser beam machinery is in the proper state and when cutting of a metal sheet is carried out under good condition by the laser beam machinery. However, if the state of the machinery, for example, the state of a generator, mirror, lens and/or assist gas of the machinery is improper, or if cutting is done under severe condition, the cut of metal sheet would be improper, resulting in gousing in which the metal sheet is not cut properly, or in burning in which the metal sheet is cut, however, causing a large amount of dross.
As grousing causes spatter which is scattered in a broad area and which may cause a fire, and as burning causes defects in the product, a worker must always stay near the laser beam machinery and watch the cutting state carefully.